1. Field of the Invention
The present invention relates to a vacuum container incorporating spacers and a method for manufacturing the same, and an image display apparatus using the vacuum container and a method for manufacturing the same.
2. Description of the Related Art
Flat display apparatuses are attracting attention as a replacement for CRT (cathode-ray tube) display apparatuses because they are thin and light. Particularly, display apparatuses in which electron emission elements and phosphors emitting light by being irradiated with electron beams are expected to have characteristics superior to other conventional display apparatuses. For example, in comparison with recently diffused liquid-crystal display apparatuses, the above-described display apparatuses are superior in that back light is unnecessary because they emit light themselves, and the angle of visibility is large.
FIG. 17 is a perspective view illustrating a display panel constituting a flat image display apparatus. In order to show the internal structure, a portion of the display panel is cut. In FIG. 17, there are shown a rear plate 3115, a side wall 3116, and a faceplate 3117 that constitute an envelope (airtight container) for maintaining the inside of the display panel to a vacuum.
A substrate 3111 is fixed on the rear plate 3115, and cold-cathode elements 3112 are provided on the substrate 3111 in the form of an N×M matrix (N and M are positive integers equal to or larger than 2, and appropriately set in accordance with a required number of display pixels). As shown in FIG. 17, the N×M cold-cathode elements 3112 are wired by row-direction wires 3113 and column-direction wires 3114. A portion constituted by the substrate 3111, the cold-cathode elements 3112, the row-direction wires 3113 and the column-direction wires 3114 is termed a multi-electron-beam source. An insulating layer (not shown) is formed between two wires at at least portions where the row-direction wires 3113 and the column-direction wires 3114 cross, in order to secure electric insulation.
A fluorescent screen 3118 comprising phosphors is formed on the lower surface of the faceplate 3117, in which phosphors (not shown) of three primary colors, i.e., red (R), green (G) and blue (B), are separately coated. A black material is formed between adjacent phosphors constituting the fluorescent screen 3118, and a metal back 3118 made of Al or the like is formed on a surface of the fluorescent screen 3118 facing the rear plate 3115.
There are also shown airtight terminals for electric connection Dx1-Dxm, Dy1-Dyn and Hv provided for electrically connecting the display panel to an electric circuit (not shown). The terminals Dx1-Dxm, Dy1-Dyn and Hv are electrically connected to the row-direction wires 3113 and the column-direction wires 3114 of the multi-electron beam source, and the metal back 3119, respectively.
The inside of the airtight container is maintained to a vacuum of about 3×10−3 Pa (10−6 Torr). As the display area of the image display apparatus increases, it becomes necessary to provide means for preventing deformation or destruction of the rear plate 3115 and the faceplate 3117 due to a pressure difference between the inside and the outside of the airtight container. An approach of increasing the thicknesses of the rear plate 3115 and the faceplate 3115 will increase the weight of the image display apparatus and produce deformation and parallax of an image when the image is seen from an oblique direction. In order to solve this problem, in the configuration shown in FIG. 17, spacers 3120, each comprising a relatively thin glass plate, for supporting the atmospheric pressure are provided. The interval between substrate 311 where the multi-electron-beam source is formed and the faceplate 3117 where the fluorescent screen 3118 is formed is usually maintained to a sub-millimeter value or a few millimeters, and the inside of the airtight container is maintained to a high vacuum, as described above.
In the image display apparatus using the above-described display panel, when a voltage is applied to each of the respective cold-cathode elements 3112 via corresponding ones of the outside-container terminals Dx1-Dxm and Dy1-Dyn, electrons are emitted from the corresponding one of the cold-cathode elements 3112. At the same time, by applying a high voltage of several hundred to several thousand volts to the metal back 3119 via the outside-container terminal Hv, the emitted electrons are accelerated to impinge upon the inner surface of the faceplate 3117. A corresponding one of the phosphors of respective colors constituting the fluorescent screen 3118 is thereby excited to emit light, whereby an image is displayed.
The spacers 3120 are efficiently arranged with a number necessary for the structure of the display panel. When disposing the spacers 3120 within an image region with a length shorter than the image region, the spacers 3120 are fixed within the image region of at least one of the rear plate 3115 and the faceplate 3117 using connecting members.
As disclosed in Japanese Patent Application Laid-Open (Kokai) Nos. 9-179508 (1997) and 2000-251796 (2000), when using spacers 3120 longer than the image region, an atmospheric-pressure-resistant structure can be obtained only by fixing both ends of the spacers 3120. At that time, a method may be adopted in which supporting members are fixed in advance at both ends of each of the spacers 3120, and the supporting members are fixed to the rear plate 3115 or the faceplate 3117 using connecting members.
The above-described display panel of the image display apparatus has the following problems.
Since a plurality of spacers are disposed in accordance with the display area of the display panel, and the thicknesses of the rear plate and the faceplate, the number of the spacers increases as the display area increases. As a result, the number of processes for disposing the spacers in the display-panel assembling process increases, thereby causing an increase in the production cost. Particularly, when disposing spacers shorter than the image region within the image region, a serious problem will arise.
When using spacers longer than the image region, it is possible to minimize the number of the spacers. However, when supporting members are fixed in advance at both ends of each of the spacers longer than the image region, and the supporting members are fixed in a state of directly contacting the substrate, accuracy in the fixed positions of the spacers and the supporting members is sometimes influenced by accuracy in the verticality of the spacers with respect to the substrate, and variations in the height of disposition when the spacers are fixed on the substrate. If a spacer is inclined by this influence, the electron trajectory from an electron emission element near the spacer may be interfered, or the electron trajectory may be distorted by disturbance of the electric field near the element, thereby influencing image display. In addition, when accommodating the spacers between the rear plate and the faceplate, a large stress may be applied to the spacers, resulting in destruction of the spacers and incapability of providing a vacuum within the display panel.
In the case of a display panel having a plurality of spacers, if the height of disposition when fixing the spacers on the substrate varies, the spacers do not contact the rear plate and the faceplate as designed, resulting in destruction of the spacers and incapability of providing a vacuum within the display panel.